Low speed discoidal electric motor

ABSTRACT

A low-speed electric motor of lightweight construction with rotor diameter greater than 500 mm, its width of a few cm, without a gearbox, with starting torque being of an order 100 Nm, it makes use of the principle of Coulomb forces. The dimensional arrangement of both the rotor and stator even at high level of torques eliminates flip-flop effect, which is typical for conventional step motors. Rotor consists of rotor disks ( 10 ) with a fixing ring ( 7 ). The carrier ( 1 ) of the permanent magnets ( 2 ) is attached to the fixing ring ( 7 ). The rotor is linked with fixing hub ( 14 ) by means of ball bearings ( 13 ) whose bearing bushings ( 12 ) are mounted with the rotor disks ( 10 ). The stator disk ( 11 ) is attached to the fixing hub ( 14 ). The segment in the shape of circular section made from soft magnetic material ( 3 ), which the coils are slid on, is accommodated in the spokes ( 8 ) fixed by the shank ( 9 ) to the stator disk ( 11 ). Relative position of every coil ( 4 ) relative to the permanent magnet ( 2 ) is monitored by the position indicator ( 5 ). The stator segments ( 3 ), which the coils ( 4 ) are placed on, making up the poles of the motor, are compensated and they are neutral from the point of view of forces F Fe  with the resultants of these forces ( 17 ), that are created by a coincidence of the permanent magnets of the rotor ( 2 ) and the segment of the stator ( 3 ) made from soft magnetic material and simultaneously compensated by zero resultant intensity of the magnetic flux ÓH=0 on the poles ( 15 ) of the segments ( 3 ) relative to the permanent magnets of the rotor ( 2 ) in all motor control modes for the reason of gradual connecting the stator coils ( 4 ) to the voltage and thanks to it no parasite forces ( 18 ) are produced bringing about the flip-flop effect and vibrations because the design engineering arrangement satisfies simultaneously the following interrelations: 
         1. The number and design engineering arrangement of the permanent magnets of the rotor ( 2 );    2. The number and design engineering arrangement of the stator segments made from soft magnetic material ( 3 ); 3. The number of the motor phases, and    4. The number and position of stator coils ( 4 ) that make up the poles of the motor installed on every segment ( 3 ) depending on the number of motor phases.

FIELD OF INVENTION

The present invention relates to a light, low-speed multipole discoidal electric motor. In particular, the present invention relates to a light, low-speed multipole discoidal electric motor which can be configured, for example, for driving collapsible wheel chairs for physically handicapped people.

BACKGROUND OF THE INVENTION

Low-speed driving units utilizing an electric motor drive are well known in the prior art. The torque of such low-speed driving units, measured on the outlet shaft at rated speed, lies within the range of units per second as being of an order 100 Nm and has been characterised by a design feature based on a standard high-speed electric drive equipped with a gearbox. However, this part of the wheel proves to have the highest failure mode.

The operation of an advanced driving mechanism requires the developement of a contactless electric motor without a gearbox to be maintenance free for the whole lifetime.

In Czech patent application 1480-97 A3 to Nicolas Wavre of Neuchatel, CH, Wavre—applies lightening of a synchronous motor with permanent magnets and by fitting coils into addendum top land, where the coils are slid on the teeth with the axes oriented to the centre of the motor, which are connected by means of a magnetic yoke. However, in Wavre's disclosure, it is not possible to attain necessary weight and performance parameters.

Czech patent CZ 279 581 B6, registrant the Institute of Thermo-technology of Academy of Sciences of the Czech Republic (Ústav termotechniky AVÈR), Prague, CZ discloses a machine with a diameter greater than one meter by applying a principle of two rotors, one of them being equipped with magnets whereas the other has pairs of pole shoes with coils slid on. This device can be used for the purpose of a light motor with a large diameter. However, it is obvious that although this arrangement cannot be used as a drive due to uncompensated flip-flop effect resulting in generating vibrations.

Czech patent CZ 291897 B6 dated 2001 discloses that conventional motors with gearboxes can be replaced by motors without gearboxes on the basis of FeNdB magnets placed on the rotor and with stator coils wound on a continuous circular ring made from soft magnetic material, e.g. ferrite where starting torque may be increased by increasing radius of the position of the electric motor functional elements. This engineering design solution is technologically limited to diameters up to 300 mm. Because of the technological limitations regarding the manufacture of the ring made from soft magnetic material, this solution cannot be applied to the manufacture of the motors with the light design engineering features without a gearbox whose diameter exceeds 500 mm, with the width being a few centimeters and with the starting torque being of an order 100 Nm, with ratio of motor diameter to the motor thickness greater than 15.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an advanced driving mechanism having a contactless electric motor without a gearbox.

It also is an object of the present invention to provide an advanced driving mechanims which is maintenance free for the whole lifetime.

It is another object of the present invention to provide a low-speed discoidal electric motor.

Additional objects, advantages and novel features of the invention will be set forth in part of the description which follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by practice of the invention.

These and other objects are achieved by providing a low-speed discoidal electric motor with permanent magnets that are fitted on the rotor and with the coils located on the stator.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood with reference to the appended drawing sheets, wherein:

FIG. 1 is an elevated side cross-sectional view of the low speed discoidal electric motor of the present invention, the cross section passing through the axis of the electric motor.

FIG. 2 depicts the origin of the parasite forces F_(Fe) from the resultant and the engineering design of the segments of the low-speed discoidal electric motor of the present invention.

FIG. 3 depicts the characteristic of the magnetic field of the permanent magnets that are in coincidence with magnetic field H of the coils of the low-speed discoidal electric motor of the present invention.

DETAILED DESCRIPTION

Referrring now to the drawings, the aforementioned shortcomings and insufficiencies are removed to considerable extent by providing a low-speed discoidal electric motor with permanent magnets (2) that are fitted on the rotor and with the coils (4) located on the stator. The stator coils (4), making up the poles of the motor, are positioned on large diameter segments that have the form of a circle section made from soft magnetic material (3) that is simply and cheaply producible. Discrete elements in the motor with permanent magnets possessing high level of magnetic remanence, with magnetic permeance unless they meet relations of coincidence of spatial dimensional arrangement that is the subject matter of this invention generate flip-flop effects, i.e. transition skips of the magnets (2) in accordance with the spatial density of the magnetic flux generated by a shape of permanent magnets of the rotor (2) and geometrical arrangement of the segments with magnetic permeance (3) together with the resultant of the sum of magnetic field intensity H of the coils (4) on the poles of the segments (15) in every position of the rotor relative to the stator.

The substance of the invention consists in a comprehensive engineering design arrangement of the active parts of the rotor, i.e. the rotor permanent magnets (2), the segments made from material of the stator (3) with magnetic permeance and the dimension and positioning of the coils of the stator (4) that make up the poles of the motor and ensures that they are neutral relative to permanent magnet (2) in terms of force and magnetic field i.e. they do not generate vibrations. In order to provide smooth motor running and to eliminate the generation of vibrations the dimensions of segments—the sections of the ring (3) in coincidence with dimensional arrangement of the permanent magnets of the rotor (2) together with dimensional arrangement of the coils of the stator (4) must satisfy simultaneously all the following relations of the geometric spatial arrangement:

-   -   1) Number of the permanent magnets of the rotor (2) must be even         number.     -   2) Outer cylindrical surface of the segments of the stator made         from soft magnetic material (3) has identical distance from the         surface of every permanent magnet (2) in every position of the         rotor relative the stator. The poles of the electric motor are         made up by the coils of the stator (4) in the air gap.     -   3) The number of segments of the stator made from soft magnetic         material (3) must not be commensurable with the number of         permanent magnets of the rotor (2) that moreover has a         characteristic defined as follows: the nearest higher as well as         the nearest lower numbers are also not commensurable with the         number of permanent magnets of the rotor (2) and both numbers         i.e. the nearest higher as well as the nearest lower numbers but         by two must be commensurable with the number of permanent         magnets of the rotor (2).     -   4) The number and positioning of the coils (4) on the segment         (3) that make up the poles of the electric motor must satisfy         the following relations:         -   1. The number of the coils (4) on the segment (3)=2× the             number of phases of the motor×N (N=integer).         -   2. Every phase of the motor must be represented on the             segment (3) by equal number of the coils (4)=number of poles             of the motor phase.         -   3. The number of the coils (4) on the segment of the stator             made from soft magnetic material (3) must be a number             commensurable with the number of permanent magnets of the             rotor (2).         -   4. The position of the coils (4) on the segment (3) must             meet a condition for angular distribution on the stator             irrespective of the dimensions and the distribution of the             stator segments made from soft magnetic material (3)             Angle of coil fitting for i-th phase=(360/number of rotor             permanent magnets)×(coil order+(i−1)n _(motor phases))             -   i=integer in the interval 1 up to n_(motor phases)             -   n_(motor phases)=the number of motor phases

For instance—for the number of permanent magnets 48 the following data meet the relations of spatial distribution for the elimination of parasite force impact that would cause vibrations:

-   -   5. 10 segments made from soft magnetic material.     -   6. 12 coils on every segment for three-phase low-speed motor, or         24 coils for six-phase low-speed motor.

FIG. 2 clarifies the origin of the parasite forces F_(Fe) with the resultant (17) that are generated by permanent magnets (2) and the engineering design of the segments made from soft magnetic material (3) and the substance of their elimination how it has been described in the above-identified items 1, 2 and 3. FIG. 3 characterizes the magnetic field (16) permanent magnets (2) that in coincidence with magnetic field H of the coils (4) induces an active force F (19) on the circumference of the motor and contemporaneously illustrates the substance of the origin of the parasite forces due to action of the sum of magnetic intensity ΣH of the individual coils (4)—poles of the electric motor inside of the stator segment (3) so that in case of not fulfilling the condition ΣH=0 induces on the poles (15) of the segments (3) parasite forces (18) in coincidence with magnetic force lines (16) of the permanent magnet of the rotor (2) whose conditions of elimination are presented in the above-identified item 4.

EXAMPLE OF THE INVENTION

The low-speed discoidal electric motor (FIG. 1) is made up of a stator and a rotor. Load bearing structure of the rotor is designed from two rotor disks (10) made from light flexible material, e.g. duralumin(ium). Both rotor disks (10) are on the outer circumference mechanically linked by means of wheel rim (7). The wheel rim (7) is intended for the creation of box-type structure of rotor sandwich arrangement. The wheel rim (7) serves in case of wheel chairs drive for physically handicapped people for tire mounting. To the inner cylindrical part of the wheel rim (7) is connected a permanent magnets carrier (1) made from magnetic conducting material. The permanent magnets carrier (1) is of annular ring shape. On the inner circular surface there are permanent magnets with high level of residual induction (2) attached. The rotor is mechanically linked to the stator by means of ball bearings (13). The ball bearings (13) are supported by bearing bushings (12). The bearing bushings (12) are mechanically linked to the rotor disks (10). The ball bearings (13) are pressed on a fixing hub (14) that is a part of the stator. To the aforementioned fixing hub (14) is attached a stator disk (11). The stator disk (11) in light sandwich design is made up of two pieces. On the circumference of the stator disk (11) there are spokes (8) mounted intended for fixing segments (3) as shown in FIG. 1. The spokes (8) for fixing segments (3) are made from non-magnetic material. The segments themselves made from soft magnetic material (3) are set into the grooves of the spokes (8) made on the circumferential surface. The lower medium part of the spoke (8) is followed by a shank (9). By means of the shank (9) the spoke for the fixing of the segments (8) attached to the stator disk (11). The segment (3) of the magnetic shield is made from soft magnetic material, e.g. transformer sheets. On the segment (3) of the magnetic shield are attached the coils (4). The active parts of the coils (4) are in the air gap. The air gap is defined by the end-face of the permanent magnet (2) and the outer surface of the segment (3) of the magnetic shield. It means that the active parts of the coils (4) are in the space through which magnetic flux of the permanent magnets (2) flows. The air gap is invariably the same in any position of rotor with regard to the stator. The poles of the stator are made up of the active parts of the coils (4) in the air gap. The number of the coils (4) underneath one permanent magnet (2) makes up the number of the phases of the motor. Relative position of every coil (4) with respect to permanent magnet (2) is monitored by position indicator (5). The coils (4) are fed with electric current lead-in wires (6) passing through hollow hub (14). Mechanical configuration of the active parts of the electric motor, i.e. the carriers (1) of the permanent magnets (2), the segment (3) of the magnetic shield including engineering design of the fixing into the spokes (8), the positioning of the coils (4) on the segment (3) of the magnetic shield and the principle of assurance of the magnetic neutrality of a segment at the moment of connecting the coils to the voltage is illustrated in detail in the FIGS. 2 and 3.

DESCRIPTION OF THE MOTOR FUNCTION

The permanent magnets (2) located along the whole inner cylindrical surface of the carrier (1) are the source of magnetic flux. The carrier (1) closes the magnetic circuit of the permanent magnets (2). On the inner side the magnetic flux enters into the air gap defined by internal cylindrical surface of the permanent magnets (2) and external cylindrical surface of the annular ring (3) of the magnetic shield. The major part of the magnetic flux (16) (FIG. 3) generates in he air gap a magnetic induction and closes through the segment (3) of the magnetic shield. The leakage part of the magnetic flux closes in the space on the inner side of the segment (3) of the magnetic shield and on the outer side of the carrier (1) of the permanent magnets (2). After connecting input power supply voltage to feeding wire (6) an electric current begins to flow through the coils (4) (FIG. 3—the electric current flowing in one direction is indicated by the character X, whereas the electric current flowing in the opposite direction indicated by the character *). The magnetic flux (16) in the air gap generates in coincidence with the magnitude and direction of the electric current flowing through that part of the winding of the coils (4) that are in the air gap the required force F (19). The previously mentioned force F is that force being transferred through the wheel rim (7) to the circumference of the wheel of the wheel chair.

The engineering design of the motor according to the paragraph Examples of the implementation of the invention” consisting in a split stator divided into segments made from the soft magnetic material generates in the point of setting in the spoke (8) a non-homogeneous magnetic field (16) producing radial forces F_(Fe) with the resultant (17) of variable magnitude according to relative position of the stator and the rotor. The course of force depends on relative position of the magnet and the axis of the spoke with the segments set in the grooves. Provided that an angle of the spoke axis (8) is a variable quantity and within the range from the beginning to the end of the magnet the force (17) reaches positive values as far as the centre of the magnet a negative values from the centre as long as the end of the magnet length irrespective of the magnet polarity. By fulfilling the following conditions:

-   -   1) The number of the permanent magnets of the rotor (2) must be         even number     -   2) The number of the stator segments made from soft magnetic         material (3) must be non-commensurable number/coprime number         under conditions according to the above-identified item 3.

Compensation of the resultant force (17) occurs due to uniform distribution of spoke axes relative to the distribution of the permanent magnets of the rotor—thanks to the method whose principle is illustrated in FIG. 2.

The condition of the magnetic neutrality of the poles of the segments (3) must be fulfilled simultaneously, it implies that the resultant intensity of the magnetic field H of the individual coils (4) of every segment (3) must meet the condition ΣH=0 so that the poles (15) of the segment made from soft magnetic material (3) in the point of setting in the spoke (8) are neutral from magnetic point of view and parasite forces (18) do not arise due to coincidence of the magnetic flux (16) of the permanent magnets (2) and the magnetic flux of the segment (3).

Individual coils (4) that make up the poles of the motor and are connected to the phase of the motor winding according to the item 4 of the paragraph “The substance of the invention” are switched to energise them in dependence of the position of the rotor relative to the stator so that radial force F (19) on the circumference of the motor may be produced. Provided that the motor construction satisfies the relations according to the item 4 of the paragraph “The substance of the invention” an even number of the coils (4) of the same phase of the motor is always energised one very segment (3) which assures that the sum of particular components of the magnetic intensity H in every point of relative position of the rotor and stator meets the condition of magnetic neutrality ÓH=0 and no parasite forces (18) between the poles (15) of the stator segments (3) and the permanent magnets of the rotor (2) occur and the motor even at low speed and high level of starting torques runs smoothly.

EXAMPLE OF INDUSTRIAL APPLICATION

The invention can be utilised providing that it works as a advanced low-speed driving mechanism to drive light portable collapsible wheel chairs for physically handicapped people or if it works as a low-speed generator intended for the production of electricity.

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto, and that many obvious modifications and variations can be made, and that such modifications and variations are intended to fall within the scope of the appended claims. 

1. Low-speed discoidal electric motor making use of the principle of Coulomb forces is characterised by light engineering structure with rotor diameter greater than 500 mm, width of few cm, without a gearbox, with the starting torque being of an order 100 Nm, where dimensional arrangement of the rotor and stator even at high levels of torque eliminates parasite force producing flip-flop effect that is typical for conventional step motors.
 2. The low-speed electric motor according to the claim 1) characterised by the fact that the poles of the stator are composed by active parts of the coils (4) in the air gap with a constant dimension along the circumference of the motor consisting of the segments of the stator in the shape of circular section made from soft magnetic material (3) and the surfaces of the permanent magnets of the rotor (2).
 3. The low-speed motor according to the claim 1) characterised by the fact that the segments of the stator in the shape of circular section made from soft magnetic material (3) on which the coils (4) are accommodated and that make up the poles of the motor, are from the point of view of forces (F_(Fe)) with the resultant force (17) that are produced by the coincidence of the permanent magnets (2) and the segments of the stator made from soft magnetic material (3) compensated in such a manner that the conditions specified further are met together, and the aforementioned conditions are as follows: the number of permanent magnets of the rotor (2) is even number, the external cylindrical surface of the segments of the stator is made from soft magnetic material (3) and it has constant uniform distance from the surface of every permanent magnet (2) in every position of the rotor relative to the stator and the number of stator segment made from soft magnetic material (3) is a co-prime number non-commensurable with the number of the permanent magnets of the rotor (2) that on the top of that has yet such property consisting in the fact that the nearest higher as well as the nearest lower number must also be co-prime numbers non-commensurable with the number of the permanent magnets of the rotor (2) and both numbers being higher and lower but by two are the numbers commensurable with the number of the permanent magnets of the rotor (2).
 4. The low-speed motor according to the claim 1 characterised by the fact that on the poles (15) of the segments (3) the sum of the intensity of the magnetic field ÓH=0 for the reason of gradual connecting the coils of the stator to the voltage so that they do not produce any parasite forces (18) generating vibrations relative to the permanent magnets of the rotor thanks to the fact that the coils (4) on the segment (3) that make up the poles of the electric motor must satisfy the relation conditions, when the number of the coils (4) on the segment (3)=2× the number of phases of the motor×N (wherein N=integer), and wherein every phase of the motor must be represented on the segment (3) by equal number of the coils (4) and the position of the coils (4) on the segment (3) must meet a condition for angular distribution on the stator irrespective of the dimensions and the distribution of the stator segments made from soft magnetic material (3), and wherein the angle of coil fitting for i-th phase=(360/number of rotor permanent magnets)×(coil order+(i−1)/n_(motor phases)) wherein, i=integer in the interval 1 up to n_(motor phases) and n_(motor phases=)the number of motor phases. 